Crystalline polypropylene has been widely used for various molding fields because of excellent mechanical property, chemical resistance and the like. However, propylene homo-polymer or random copolymer with small amount of α-olefin has high stiffness, but may be deficient in impact resistance.
Therefore, methods for adding rubber components such as ethylene-propylene copolymer (EPR) to propylene homo-polymer, or production of so-called impact copolymer containing rubber components by copolymerizing propylene and ethylene or α-olefin successively after homo-polymerization of propylene, has been employed for improvement of impact resistance. Further, by increase of rubber content of this impact copolymer, flexibility and impact resistance can be improved.
As another problems different from these points, in the impact copolymer obtained by polymerization in the presence of conventional Ziegler-Natta type catalyst, component of low molecular weight (oligomer component and the like) is present due to the nature of catalyst. In particular, recently, there is a tendency for further improving moldability of the obtained impact copolymer by increasing the flow property.
However, when flow property of rubber parts is enhanced too much, production ratio of low molecular weight component increases along with this, consequently, it has been known that this low molecular weight component becomes the causes of the various problems that generation of smoke, unusual malodor and the like are caused at molding, and even after molding, adverse effect is affected to odor or taste, and anti-blocking property is deteriorated by sticking, and the like. When powder properties of polymerized polymer are deteriorated, stable production cannot be achieved, therefore, this is a problem. On the other hand, when difference of average molecular weight of crystalline polypropylene and rubber parts becomes large, problems that evolution of gel increases at molding or linear expansion rate becomes high, are caused.
On the other hand, it has been known that isotactic polypropylene can be obtained by polymerizing propylene using metallocene type catalyst different from the conventional Ziegler-Natta type catalyst. In addition, it has been known that the impact copolymer can be produced by copolymerizing ethylene and propylene successively after homo-polymerization of propylene using similar catalyst (for example, refer to Patent Reference-1, 2). Further, the impact copolymer excellent in stiffness and impact resistance has been disclosed (for example, refer to Patent Reference-3).
In particular, in the impact copolymer, in order to exhibit high impact resistance, it is necessary to show, for example, lower glass transition temperature and in order to satisfy this, copolymerization of propylene and ethylene or α-olefin is preferred to be carried out so that each contents of these can satisfy some ranges (for example, refer to Non-Patent Reference-1).
And, many examples of transition metal compounds constituting the above-described metallocene type catalysts have already been known. Particularly, in order to improve the stiffness of the impact copolymer, also, transition metal compounds which provide the homo-polypropylene having high melting point have been known already (for example, refer to Patent Reference-4).
However, when these propylene type impact copolymers are produced by using metallocene type catalyst, the following technical problems have been occurred due to the reactivity difference of propylene and the other co-monomers.
That is, when copolymerization of propylene and ethylene or α-olefin is carried out by the conventional method using metallocene type catalyst after homo-polymerization of propylene, gas composition ratio of propylene/(ethylene or α-olefin) in polymerization atmosphere is greatly different from the polymerized amount ratio of amount of propylene/(amount of ethylene or amount of α-olefin) polymerized in this atmosphere, and the case of decreasing the polymerized amount of (ethylene or α-olefin) in the polymer is occurred. That is, in order to obtain the copolymer having the desired content of ethylene or α-olefin, monomer gas having the greatly different monomers ratio from the contents of monomers in copolymer is needed to provide to polymerize, and it was the problem on the production. Further, in the extreme case, copolymer having the desired contents could not be produced due to restriction of the polymerization equipment.
Thus, in catalyst using metallocene complex, difference of ethylene content in ethylene/propylene mixed gas and ethylene content in the polymer becomes large, therefore, development of the production method having high uptake efficiency of ethylene and α-olefin for resolving these problems is needed.
In addition, the case of using the metallocene catalyst known until now has a problem that when copolymerization of propylene and ethylene or α-olefin is carried out in gas-phase, molecular weight of the resulting copolymer is low. In propylene-ethylene block copolymer, molecular weight of the copolymer is needed to keep more than a certain level to exhibit high impact resistance, and also, the production method by which the copolymer having high molecular weight can be produced is desired. In addition, in order to reduce the catalyst cost per unit polymer or to increase the content of rubber part, development of the catalyst having high rubber activity have been desired.
On the other hand, Patent Reference-5 describes the complex having a substituent at 5-position of indenyl ring, and discloses the metallocene complex by which propylene homo-polymer and copolymer having high melting point and high molecular weight can be provided.
However, this is the method having low uptake efficiency of ethylene, and it is not possible to recognize that polymerization performance such as melting point of resulting homo-polymer, and polymerization activity are satisfactory, further high-performance metallocene complex is desired to be created.